The present invention relates to electrically operated valves of the type employed for controlling expansion of fluid flowing in a fluid flow system. In refrigeration or air conditioning systems, electrically operated expansion valves can be used to control the flow of refrigerant to the evaporator or endothermic heat exchanger in order to maintain the desired amount of superheat of the refrigerant discharging from the evaporator. Heretofore, it has been common practice to employ a mechanical thermally responsive expansion valve for controlling refrigerant flow to the evaporator in a refrigeration or air conditioning system. Mechanical thermostatic expansion valves typically employ an hermetically sealed liquid filled chamber which senses the temperature of the refrigerant discharging from the evaporator; and, the temperature changes in the liquid cause expansion and contraction thereof, the forces of which are applied to a pressure responsive diaphragm for moving a valving element to control the flow in the line to the evaporator. Mechanical thermostatic expansion valves have experienced widespread use but have the disadvantage of being only reactive to a temperature in the system and not anticipatory of the ambient conditions. Additionally, mechanical thermostatic expansion valves are subject to deterioration of the hermetic sealing of the chamber over prolonged usage and loss of fluid from the chamber. Thus it has been desired to provide for electrical control of the refrigerant expansion valve in refrigeration and air conditioning systems, particularly air conditioning systems utilized in motor vehicles where the rate of change ambient conditions and thermal loading is relatively high.
Accordingly, it has long been desired to provide a simple design for an electric valve suitable for control of the expansion and flow of refrigerant and which is reliable and low in manufacturing costs and which may replace mechanical thermostatic expansion valves.